Currently, a wide variety of building blocks or modules are available for construction of retaining walls to hold back or support earth or other fill material, each tailored to a particular use. Generally, a retaining wall may be constructed with building blocks made from natural sources such as timber, granite or stone, or with man-made materials such as concrete. Man-made materials typically cost less than most natural materials and are more versatile since they may be formed to desired shapes and configurations.
In recent years, the modules used for construction of retaining walls typically comprise concrete. Concrete has a relatively high density (e.g., 1950 kg/m3-2250 kg/m3 (120-140 lbs/ft3)). Because of this high density, even relatively small modules can be quite heavy. For example, a concrete block which is 40 cm (16 inches)×30.5 cm (12 inches)×20 cm (8 inches) may weigh 45 kg (100 lbs) or more.
When retaining walls are constructed from concrete modules, the building blocks are typically placed in a side-by-side relation in layers or courses, in which a block on a second course overlaps two blocks on the first course, thereby providing structural support and stability. Many blocks, such as those shown in U.S. Pat. Nos. 4,379,659, 4,671,706 and 5,072,566 have troughs in which fill (e.g., earth, sand or gravel) can be packed to increase the weight of the block and provide an additional stabilizing force which prevents the relative movement of the blocks. To provide additional support, the blocks may be constructed with pins which hold the courses secure relative the courses disposed beneath and above. Other methods for supporting the retaining wall employ a geo-grid mesh which may be placed between courses of or otherwise mechanically connected to blocks with the grid running into the earth or other fill material behind the wall.
Also, in forming the retaining wall, the blocks may be stacked such that they form a set back (the angle of the wall relative to a horizontal plane) of less than ninety-degrees as viewed from the side. Many blocks, such as those disclosed in U.S. Pat. No. 4,671,706, are limited in the degree of set back they are capable of attaining. Depending on the landscaping requirements, it may be necessary to build the wall with a wide range of set back angles, typically from forty-five to ninety degrees relative the horizontal plane.
The individual modules forming the retaining wall system are typically substantially rectangular in shape, comprising a front, two side walls, and a bottom forming a single compartment that is open on its top, and may be filled with gravel, soil, and/or vegetation. See, for example, U.S. Pat. Nos. 5,277,012, 5,658,098, D340,996, D347,285, D360,475, D362,077 and D372,106. Vegetation is sometimes planted to provide a natural appearance and/or to partially cover the wall. Often the units have a front face that has a greater height than the side walls.